The present invention relates to a rotary machine and more particularly to a tie bolt and stacked wheel assembly for the rotors of such machines, wherein the tie bolts retain the stacked wheels in assembled relation without relative rotation between the tie bolts and the stacked wheels. Exemplary rotary machines to which this invention relates include turbines and/or compressors.
The rotors of rotary machines, such as turbines and compressors, are typically formed of axially stacked wheels, which hold individual blades about their periphery. For example, compressor rotors include a series of individual compressor wheels stacked together with a set of tie bolts extending generally axially through the stack. The wheels mount the blades which, together with stator blades, form the compressor stages. The tie bolts are typically elongated studs threaded at both ends for receiving nuts to maintain the wheels in stacked, assembled relation relative to one another. It will be appreciated, however, that tie bolts can have a headed end. In many such rotors formed of stacked wheels, the stacked wheels have ridge and groove arrangements along their interfaces so that the rotor torque can be carried through the stack. In a preferred form, however, sufficient clamp load is applied to the tie bolts to ensure that the rotor torque is carried through the stack by friction between the faces of the wheels and the nut faces.
It will be appreciated that any loosening of the nuts on the tie bolts would clearly reduce the tension on the bolts and, thus, lower the torque carrying capability of the rotor, eventually to unacceptable levels. Recognizing this problem, current design practice requires that the rotation of the nut relative to the bolt be prevented by redundant methods. One such method relies on the nut face friction against the threads and the stack. A second method of preventing rotation of the nut relative to the bolt is to run a jam nut against the primary nut to prevent its rotation relative to the stud.
It is also desirable to prevent rotation of the tie bolt assembly relative to the stacked wheels to facilitate assembly and ensure sufficient clamp load can be applied for rotor torque to be carried through the stack. A need remains for a reliable bolt and nut assembly mechanism that remains rotationally locked and assembled at all times to keep, e.g., the compressor wheels fully engaged during all operating conditions and in a manner which will not damage the tie bolt assembly or rotor.
The invention provides a simple and reliable bolt and nut mechanism for holding e.g., the aft nut of a compressor during assembly operations and also that remains assembled at all times to keep the compressor wheels fully engaged during all operating conditions.
In an embodiment of the invention, a tie bolt and stacked wheel assembly for the rotor of the rotary machine is provided wherein the stacked wheels are joined one to the other in an axial array by tie bolts, more specifically studs, provided at opposite ends with nuts to define bolt assemblies. To prevent rotation of the stud and nut combination within the rotor, a self-locking nut is provided at the aft end of the stud.
Thus, the invention may be embodied in a self locking nut comprising: a main body; a forward radial flange defined at a first longitudinal end of said main body; an aft radial flange defined at a second longitudinal end of said main body; and a tab component projecting radially from a radially outer peripheral surface of said aft radial flange.
The invention is also embodied a stacked wheel assembly for the rotor of a rotary machine comprising: a plurality of stacked wheels for rotation about a common axis and forming part of the rotor; and a plurality of elongated tie bolts passing through aligned bolt holes of said stacked wheels for retaining the wheels in axially stacked relation, said plurality of tie bolts being spaced from one another circumferentially of the rotor; at least one of said tie bolts comprising a stud having a locking nut at least one of mounted to and defined at one longitudinal end thereof, said locking nut comprising at least one tab component projecting radially therefrom, wherein an end face of said plurality of stacked wheels includes a receptacle for receiving said locking nut and said at least one tab component.
The invention is further embodied in a method for retaining stacked wheels for the rotor of a rotary machine in an assembled relation comprising: stacking a plurality of wheels so as to align bolt holes respectively defined therethrough, to thereby define a plurality of tie bolt passages axially of said stacked wheels; providing at least one tie bolt comprising a stud having a locking nut at least one of mounted to and defined at one longitudinal end thereof, said locking nut comprising at least one tab component projecting radially therefrom; inserting said stud through a said tie bolt passage defined by aligned bolt holes of said stacked wheels; disposing said locking nut and said at least one tab component in a receptacle defined in an end face of said plurality of stacked wheels; and axially fixing said at least one tie bolt to said stacked wheels.